1. Technical Field
The present invention relates to a motor control device that can shorten a cycle time of a machine.
2. Description of Related Art
In a machine such as a machine tool which performs processing, not only an improvement of a processing quality but also a shortening of a cycle time is required. In order to shorten the cycle time, it is necessary to reduce a processing time by improving a tracking performance at the time of processing, and to quickly return to the original position by a speedup of the positioning when the processing is finished.
The tracking performance at the time of processing is improved by increasing a feedback control gain. On the other hand, the speedup of the positioning when the processing is finished is realized by a control in which a rigidity of the machine is taken into consideration.
In many cases, when the positioning is performed at a high speed, a vibration occurs due to the lack of the rigidity of the machine. For this reason, a vibration controller is mounted on the motor control device, which can shorten a setting time of the positioning by suppressing the vibration of the machine.
Japanese Unexamined Patent Application Publication No. 2010-41734 is disclosed as a technology that realizes the speedup of the positioning by the vibration control. In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2010-41734, using a machine base model, a vibration control is performed in the model control system side so that the vibration of the machine is suppressed, and an instruction for suppressing the vibration is provided to the feedback control system side from the model control system side.
However, since phase characteristics of the model control system are not linear, it is not possible to use the model control system at the time of trajectory control such as in the processing. Therefore, at the time of trajectory control, the feedback control system is used while the model control system is not used.
In order to shorten the cycle time of the machine in the technology disclosed in Japanese Unexamined Patent Application Publication No. 2010-41734, it is necessary to switch the model control system and the feedback control system to the time of trajectory control and the time of positioning control. However, even though the control system is quickly switched, there is a possibility of occurrence of a position shift in the positioning of the feedback control system due to the control delay in the model control system.
The reason for the above is because an amount of model position change output from the model control system is the position instruction in the feedback control system, but even though an amount of position instruction change to the model control system becomes zero, the amount of model position change does not become zero quickly. When the model control system is switched to the feedback control system in a state in which the amount of model position change remains, the remaining portion of the amount of model position change becomes the amount of position shift in the feedback control system. Particularly, in a case where the vibrational frequency of the vibration is low, since a gain in the model control system cannot be high, it takes a considerable amount of time until the model position shift becomes zero.
Therefore, in the related art, in order to avoid the position shift in the feedback control system, the control system has to be switched from the model control system to the feedback control system after the amount of change of the model position becomes zero, and thus, it is not possible to speedup the switching of the control system.
Japanese Unexamined Patent Application Publication No. 2005-198404 discloses a technology by which the switching of the control system can be realized. The technology disclosed in Japanese Unexamined Patent Application Publication No. 2005-198404 includes an identification unit that identifies the model of a control target by identifying characteristics of the control target, and a controller selection unit that outputs a selection signal based on the identified model. One feed-forward controller is selected from a plurality of feed-forward controllers and a position instruction is input to the selected feed-forward controller. One feedback controller is selected from a plurality of feedback controllers by a selection signal and a feed-forward signal and a position detection signal are input to the selected feedback controller, and the torque instruction is output. A current control is performed using the torque instruction and the control target is operated by driving the motor.